1. Technical Field of the Invention
This invention relates to mobile telecommunication systems and, more particularly, to a system and method of supervising proper frame and time slot synchronization between radio base stations and mobile stations in a mobile telecommunications network.
2. Description of Related Art
Personal Communication Services (PCS) is a synchronous data communication service to be offered as an end-user communication service for mobile subscribers. IS-136.2, one of the standards for PCS operations, requires a common source for synchronization of symbol and Time Division Multiple Access (TDMA) frame and time slots with an absolute frequency tolerance of approximately +/-5 parts per million (ppm) (translated to Stratum 3E). IS-136.2 is hereby incorporated by reference herein. Future services are expected to include more digitized data as services include more data transfer and video with real-time capabilities in addition to voice. Tolerances tighter than the +/-5 ppm of IS-136.2 may be required for some applications. A strong need therefore exists to define Operation and Maintenance (O&M) objects that are capable of properly supervising synchronization between base stations and mobile stations.
The current synchronization source for mobile telecommunications networks is classified as Stratum 4 at the user end, and its accuracy has been adequate for voice and most data communications. However, communications such as high definition video require a more accurate synchronization source. There are several alternative sources for network synchronization which provide better accuracy than Stratum 4 at the user end. These sources, in order of decreasing accuracy, include the Global Positioning System (GPS), the Loran-C navigation system, and SONET Digital Hierarchy (SDH) O&M. Each of these synchronization sources provides a different level of accuracy, and the more accurate sources are generally more expensive to implement, access, and utilize as synchronization sources for mobile telecommunications networks. To date, service providers have not offered the more expensive synchronization sources at the user end because there is no billing structure set up to charge their subscribers for the increased cost of operation, and the service providers do not want to pay for the increased capability themselves.
One solution to the problem of providing adequate synchronization for all service applications is to implement the most accurate synchronization source and utilize it for all applications. However, this solution is very expensive, and generally provides a more accurate source than most service applications require. With this solution, subscribers utilizing applications with less stringent requirements would pay unnecessarily high rates because of the higher synchronization cost. Subscribers utilizing service applications requiring the tightest synchronization tolerance, on the other hand, would be subsidized by the subscribers having less stringent requirements since payments from the other subscribers help pay for the synchronization source.
It would be advantageous to have a system in a mobile telecommunications network that provides required levels of synchronization while overcoming the inequities of existing solutions regarding cost to subscribers. The present invention provides such a system.